1. Field of the Invention
The invention relates to a solder joint material and a method of manufacturing the solder joint material, a soldering member and a solar cell module.
2. Description of the Related Art
If a bare copper is used as a soldering member, an oxide film formed hinders wetting of the solder and this results in poor solder bondability.
In addition, a brittle intermetallic compound (Cu6Sn5) layer is formed at an interface between copper and Sn-based solder due to heat during soldering. Cu6Sn5 is a hexagonal crystal at high temperature but transforms into an orthorhombic crystal at low temperature. This causes cracks, etc., to develop and decreases joint reliability after soldering. This applies not only to bare copper but also to Sn-plated copper or Sn-based solder-plated copper. In products of Sn-plated copper or Sn-based solder-plated copper which are subjected to heat during soldering or are used at high temperature, Cu6Sn5 formed during hot-dipping further grows due to heat applied to use the products.
To prevent such a problem, WO2009/051255 discloses obtaining an interface compound (Cu,Ni)6Sn5 by adding an appropriate amount of Ni to the solder so as to prevent the occurrence of cracks based on the concept that the hexagonal crystal is stable even at room temperature.